This invention relates to a belt driven camshaft arrangement for an internal combustion engine and more particularly to an improved arrangement for insuring a long belt life without trouble.
In connection with the use of overhead camshafts for internal combustion engines, a wide variety of mechanisms have been employed for driving the camshafts from the engine crankshaft. There are a number of advantages to driving the camshafts by means of toothed belts as opposed to the gear or chain drives formerly used for this purpose. A toothed belt offers the advantage of simplicity, silence and also does not require lubrication. It is, of course, desirable to provide a long life for the driving belt so that high service intervals are possible and maintenance for the owner is reduced. In order to achieve this goal, it is important, among other things, to avoid excess heat being applied to the belt.
It is, therefore, a principal object of this invention to provide an improved arrangement for driving the camshafts of an internal combustion engine.
It is a further object of this invention to provide a valve driving arrangement for an internal combustion engine using a flexible toothed belt and a cooling arrangement for insuring that the belt is operated at a temperature that will offer a long life.
One way in which the belt life may be lengthened is by placing the belt is a protective casing. However, it must be insured that this casing does not permit the belt to become heated.
It is a further object of this invention to provide an improved protective casing for the belt drive of an engine valve train.
It is a further object of this invention to provide a heat insulating belt housing for the valve drive of an internal combustion engine.
In connection with the use of toothed belts for driving the valve train of an internal combustion engine, it is also desirable to protect the belts from contamination. Therefore, the enclosure of the belt within a protective housing will achieve this purpose but, as has been noted, this can present some problems in connection with maintaining the belt at a normal operating temperature. This cooling of the belt can be accomplished by providing an air flow path through the belt casing. However, the provision of an air flow path can give rise to the intrusion of foreign material into the belt casing that can damage the belt.
It is, therefore, a still further object of this invention to provide an improved belt casing arrangement having a ventilating device that will insure against the intrusion of foreign material into the belt casing.
When a valve drive belt is contained within a protective casing, it is further desirable if an arrangement can be incorporated for circulating air through the casing in order to cool the belt. However, the provision of a fan drive can give rise to difficulties in connection with the location and driving of the fan. Specifically, the drive for the fan and the fan location should be such that the size of the engine is not considerably enlarged.
It is, therefore, a still further object of this invention to provide an improved, compact driving arrangement for a fan for cooling the drive belt of an internal combustion engine valve train.
A number of accessories are also driven off the engine and frequently some of these accessories may be driven from the same drive belt as the valve train. Some of these accessories can benefit from the positioning within a drive belt casing since this will protect these accessories also from foreign material.
It is, therefore, a still further object of this invention to provide an improved accessory drive arrangement and protective casing for an internal combustion engine.
In connection with the use of drive belts or drive chains, it is also desirable to maintain the proper tension on the flexible transmitter that drives the camshaft. This is due to the fact that flexible transmitter, be they either drive chains or toothed belts, tend to elongated with age. Therefore, a wide variety of automatic or tensioning devices have been employed for maintaining the proper tension on the transmitter when such elongation occurs. However, the type of tensioners previously employed add significantly to the size of the engine.
It is, therefore, a still further object of this invention to provide an improved and compact flexible transmitter tensioner for the camshaft drive of an internal combustion engine.
It is a further object of this invention to provide a compact tensioner for a toothed driving belt of an engine.